It is often a requirement to include payloads, such as weighting or instrumentation devices within the interior of a wing. Such payloads are typically carried within enclosures that are installed in the interior of a wing. For example, in rotorcraft, ballast weights may be installed in an enclosure which is placed inside the interior of a rotor blade, in order to balance the blade.
Typically, such enclosures are held in place using fasteners, adhesive bondlines, or through other means of coupling such enclosures to the interior of the wing. Due to the various stresses during flight, fatigue can be induced in the bondlines or fastener threads. Reduction of these stresses or elimination of parts that fatigue are a benefit to an air vehicle's lifecycle and safety.
In a rotorcraft, having the enclosures near the tip and as far from the pitch axis as possible allows for maximum effect on inboard and outboard static balancing as well as fore and aft dynamic balancing. Unfortunately, advanced composite rotor blades often use complicated tip designs including anhedral, dihedral, sweep and taper to increase aerodynamic performance, therefore sizing enclosures within these features may be difficult. In addition, due to loads environments that cause bending and twisting of the blade during flight, simply moving the enclosures inboard may expose the bondlines and or fasteners to increasingly higher bending stresses; therefore sizing the bondlines and fasteners may be more difficult.
Several attempts have been made in the past to solve the issue of how to locate an enclosure within the interior of a rotorblade. While these attempts may have their advantages in some situations, they may not be advantageous in others. One such attempt includes moving enclosures further inboard on the rotor blade. However, moving the adjustable weight enclosures inboard and away from the rotor blade tips may lead to other difficulties, such as issues related to cutting an access panel through a load bearing structure and issues related to bonding or bolting a stiffer enclosure to a more flexible structure.
Another attempt includes the use of removable tips. However, these may be an expensive option and can increase the weight of the blade. Another attempt includes co-bonding an enclosure with a composite rotor blade. However, a co-bonded enclosure may restrict pressure application during cure which may affect laminate quality, may prohibit certain non-destructive inspection techniques and may make it more difficult to control the location.
Therefore, a solution is required for installing enclosures into the interior of a wing, while avoiding the difficulties associated with bonding or bolting a stiffer enclosure to a more flexible structure in wing locations which experience relatively high levels of mechanical stresses.